The present invention relates to networks having multiple access (MA) segments and in particular Internet Protocol (IP) networks having MA segments over which multiple end systems communicate over the MA segment with one switching node. The MA segment can, for example, be any satellite, local multi-point distribution system, wireless LAN or cable modem system which uses IP quality of service (QoS) and has a switching node that can broadcast or multicast packets to all end systems and receive packets from all end systems. The end systems can be end user terminals, gateways between the MA segment and other networks or they can be interfacing switches between the MA segment and multiple end user terminals.
Such MA segments will generally operate in accordance with a layer It protocol, such as asynchronous transfer mode (ATM), frame relay or ethernet and will provide (QoS) levels required by the packets sent over the segment. Here the term packets is used to denote any parcel of information which is transmitted over such MA segments, for example ATM cells, Frame Relay Protocol Data Units or Ethernet Packets. In such systems each end system requires a different connection identifier or label, per QoS class and per next hop (or intermediate) destination, in order to communicate with the switching node. If there are many end systems, for example 10,000 end systems, 20 next hop destinations from the switching node and three QoS classes, then 60,000 different labels will be required. These labels will necessarily be relatively long and will therefore take up a lot of space in the headers of the packets transmitted over the MA segment, which space is a scarce resource. The large number of labels results in a large and complex routing table which has to be used by the switching node. Also, because each end system requires its own set of labels, label muting information has to be distributed to each end system individually which takes up signalling resource in the MA segment.
The object of the invention is to reduce the number of labels used in such MA segments in order to reduce the size of the labels so that they take up less space in each packet transmitted over the MA segment and to reduce the size and complexity of the routing table used by the switching node. A further object of the invention is to reduce the number of packets that have to be transmitted over the MA segment in order to distribute the labels so as to reduce the amount of signalling resource taken up by label distribution.
According to the present invention thee is provided a communication system having a multiple access segment, which comprises a plurality of end systems and a switching node configured such that each end system can transmit packets over the MA segment to the switching node and such that the switching node can transmit packets over the MA segment which packets are received by all the end systems and the system operates in accordance with a protocol which provides a quality of service to the packets transmitted over the MA segment, wherein the number of labels used for switching by the switching node is limited to the number of intermediate (or next hop) destinations available to the switching node multiplied by the number of quality of service classes offered by the protocol.
There is also provided a communication system having a multiple access segment, which comprises a plurality of end systems and a switching node configured such that each end system can transmit packets over the MA segment to the switching node and such that the switching node can transmit packets over the MA segment which packets are received by all the end systems and the system operates in accordance with a protocol which provides a quality of service to the packets transmitted over the MA segment, wherein the switching node comprises means for collating primary label routing information for packets to be transmitted across the MA segment from the end systems such that each primary label is dependent on the intermediate destination of the packet and the QoS requirement of the packet and is independent of the end system from which the packet originates and the switching node switches packets using only the primary label.
In this way the number of labels used for switching by the switching node is much reduced. This number is significantly less than in known systems which allocate separate labels to each end system, per intermediate destination and per QoS class. This means that less space in each packet header is used for the primary label and that the label routing information, usually in the form of a routing table, used by the switching node and communicated to the end systems is less complex than in known systems. Also, because the label routing information is independent of the end system from which a packet originates, the same label routing information can be sent to each end system. Thus, the switching node can send the same packets of label routing information to all the end systems which packets will be received by all the end systems. In previous systems different label routing information was sent to each end system and so many more packets had to be sent over the MA segment in order to provide all the end systems with label routing information. Accordingly, the present invention significantly reduces the amount of signalling resource within the MA segment which is used for distributing label routing information to the end systems.
The MA segment may comprise a broadcast downlink over which the switching node transmits packets to the end systems or alternatively may comprise a multicast link over which the switching node transmits packets to the end systems.
The switching node will generally comprise at least one headend which receives incoming packets and a switch, more specifically, a label switch router (LSR), which can switch packets received from the end systems to intermediate or next hop destinations based only on the primary label. Part of the switching node, such as part of the switch, for example a switch controller may be located remotely from the headend.
As an alternative to, or in addition to, the switching node transmitting the primary label routing information, generally in the form of a routing table, to the end systems by broadcast or multicast, the end systems may comprise means for making on demand requests for primary labels from the switching node which requests set out the destination and the QoS required for a packet and the switching node comprises means for transmitting to all the end systems a set of label routing information including a mapping between the requested destination and QoS and the primary label. The set of label routing information sent may comprise the whole or a part of the label routing information for ad destination and QoS pairs. Because the set of information is received by all end systems, all the end systems will be able to use the set of information they receive to update their primary label routing information, thus reducing the number of on demand requests made by end systems across the MA segment which reduces the number of packets which have to transmitted across the MA segment in order to transmit the label routing information to all the end systems. This on-demand type of label distribution may be required if the broadcast or multicast is not totally reliable or if an end system becomes active just after the switching node has sent label routing information to all the end systems. Label routing information may be transmitted by the switching node at pre-determined time intervals or these transmissions may be event driven or driven by the network control policy for the communication system.
As the QoS required by a packet can be inferred from its primary label a scheduler on the switching node may use the primary label for scheduling.
The multiple access segment may be a satellite segment, a local multipoint distribution system, a wireless local area network or a cable modem network. Where the MA segment is a satellite segment, the switching node may include a satellite.
The present invention is particularly useful in communication systems which operate in accordance with an internet protocol.
Where the communication system operates in accordance with an internet protocol and the multiple access segment operates in accordance with an ATM protocol, the end systems may comprise segmentation means for segmenting an internet protocol packet into ATM cells and for locating the primary label in the VPI/VCI space of the ATM cell header.
Where the communication system operates in accordance with an internet protocol and the multiple access segment operates in accordance with frame relay, the end systems may comprise segmentation means for segmenting an internet protocol packet into frame relay Protocol Data Units (PDUs) and for locating the primary label in the Data Link Connection Identifier (DLCI) space of the frame relay PDU header.
Where the communication system operates in accordance with an internet protocol and the multiple access segment operates in accordance with a layer if media encapsulation protocol that has no native label structure (such as Ethernet Protocol or Point to Point Protocol (PPP)) the end systems may comprise encapsulation means for encapsulating an IP packet including means for locating the primary label in a shim header of the encapsulated IP packet.
According to a second aspect of the present invention there is provided a method of communication over a multiple access segment, which segment comprises a plurality of end systems which can transmit packets to a switching node and the switching node can transmit packets which packets are received by all the end systems, and the MA segment operates in accordance with a protocol which provides a quality of service requested by the end systems for the packets transmitted over the segment, wherein the number of labels used for switching by the switching node is limited to the number of intermediate destinations available to the switching node multiplied by the number of quality of service classes offered by the protocol.
There is also provided a method of communication over a multiple access segment, which segment comprise a plurality of end systems which can transmit packets to a switching node and the switching node can transmit packets which are received by all the end systems, and the
MA segment operates in accordance with a protocol which provides a quality of service requested by the end systems for the packets transmitted over the segment, wherein the method comprises the steps of;
collating primary label routing information for packets to be transmitted across the MA segment from the end systems such that each primary label is dependent on the intermediate destination of the packet and the QoS requirement of the packet and is independent of the end system from which the packet originates, and
switching packets from the end systems to the intermediate destinations at the switching node using only the primary label.
The method according to the second aspect of the present invention has the same advantages and preferred features mentioned above in relation to the communication system according to the first aspect of the present invention.
According to a third aspect of the present invention there is provided a switching node for a communication system having the features of the switching node of the communication system according to the first aspect of the present invention.
According to a fourth aspect of the present invention there is provided an end system for a communication system having the features of the end systems of the communication system according to the first aspect of the present invention.